Fusion is typically characterized by a wave complex formed by depolarization of the myocardium initiated by two different foci, commonly a non-native stimulus as from a pacemaker or ICD and a native stimulus. Pseudofusion is typically characterized by a wave complex formed by depolarization of the myocardium initiated by a native stimulus; however, a non-native stimulus, that does not contribute to depolarization, is present and distorts the wave complex.
Various fusion and/or pseudofusion scenarios may cause a pacing device to waste power and to deliver non-optimal or inadequate therapy. In particular, fusion and/or pseudofusion may cause a pacing device to deliver a stimulus where native activity would suffice. In addition, in a pacing scheme that implements a ventricular autocapture algorithm to set a ventricular stimulus power level, fusion, and/or pseudofusion may cause the algorithm to set too high of a ventricular stimulus power level. To minimize the risk of setting an inappropriate power level, various ventricular autocapture algorithms rely on some degree of fusion and/or pseudofusion avoidance algorithms. For example, if non-capture is diagnosed following a primary stimulus pulse, then a back-up pulse is delivered and, on the next cycle, the AV delay (or PV delay) is extended (e.g., by approximately 100 ms). An inference is then made that the diagnosed loss of capture is due to fusion if a native R wave is detected within this extended AV delay.
While autocapture algorithms that account for fusion and/or pseudofusion exist, they are generally limited. Thus, a need exists for recognition algorithms that can more accurately recognize fusion and/or pseudofusion. Various exemplary methods and/or devices are described below which may address this need and/or other needs.